High vacuum gate valves are typically employed in extreme environments, such as are encountered in fabrication processes of integrated circuit semiconductors, for example. Other processes involving technologies such as low pressure chemical vapor deposition: sputtering, plasma, and the like, also require high vacuum joints in piping and reliable high vacuum gate valves. Such joints and valves are typically formed of high corrosion resistance materials such as stainless steel, and they may be adapted for operations at very high temperatures.
High vacuum gate valves typically provide for actuation from the ambient, ideally with no loss of vacuum level. Annular metallic sealing surfaces for such valves have been successfully provided in the past. One such annular sealing surface is illustrated in U.S. Pat. No. 3,208,758, a salient feature of which is reproduced herein as FIG. 1.
Annular sealing surfaces, such as the one illustrated by the FIG. 1 flange 10, have been found to be readily formable because such surfaces, like the protruding portion 12 of the FIG. 1 flange 10, and the inwardly adjacent flat portion 14 and outwardly adjacent vertical wall 16 thereof, may be created by turning the flange workpiece relative to, and machining with an appropriate cutting tool or bit of a metal lathe.
Generally rectangular sealing surfaces, such as the one illustrated in FIG. 2 herein, have proven to be very difficult to fabricate with prior art techniques. In FIG. 2 a rectangular flange 20 defines a generally rectangular sealing surface 22, and the inside peripheral ridge 24 of which forms a twenty degree angle with the plane of the sealing surface 22 of the flange 20. The inwardly rising ridge 24 is typically formed by end milling of the flange with a mill. In order to provide the sealing surface 22 with necessary clearance immediately outside the ridge 24 into which the gasket metal will flow under extreme clamping pressure, the prior practice has been to mill perpendicular slots 26, 28 all away across the flange, as shown in FIG. 2. The major drawback of this approach has been that at the corners 30, where different milling directions intersect, hand burnishing and polishing has been required in order to achieve the precision needed to achieve a high vacuum seal. A cold welded rectangular copper wire gasket was placed onto the sealing surface 24 and was caused to flow throughout the sealing area defined by the flange 20 and its complementary mating flange by virtue of extreme clamping pressure applied between the two flanges as by multiple bolts. The seals resultant from flanges formed like the flange 20 were not always reliable, and often developed leaks.
One high vacuum valve construction employing a generally rectangular sealing surface at the gate is depicted in U.S. Pat. No. 3,212,036. The generally rectangular sealing surface of the gate, which engaged a metal gasket material, was formed as a separate element from the gate and was subsequently welded onto the gate structure. One problem with welding of parts to the gate element is that it causes the gate to warp or buckle and thereby lose its precisely specified geometry and fail to achieve a reliable high vacuum seal.
Another generally rectangular sealing surface employed in the prior art is illustrated in FIG. 3. Therein, a flange 40 includes an inwardly rising ridge 42 and a very wide recessed sealing surface 44 bounded by an outer wall 46. The width of the surface 44 was required by the fact that the end milling tool used to machine the slanted surface of the projecting ridge 42 had to clear the top of the wall 46 while the slanted surface. This created a severe problem in that the swaging pressure upon the copper gasket material generated by the ridge 42 as the flange 40 was clamped to its mating flange, failed to cause the copper gasket to flow all the way to the back wall 46. This failure resulted in a tendency of this prior joint to develop leaks. In addition, the copper gasket had to be formed around bolt openings 48, further increasing the tendency of this prior design to leak.